Properdin and Factor B have been purified, labelled and found to be functionally active. C3 has been purified and in the near future will be radiolabeled, retested for functional activity and the absence of bacterial or pyrogen contamination demonstrated. These purified labelled protein will be used to perform turn-over studies in a series of patients with SLE, discoid lupus and control individuals, and correlated with serologic parameters and immunofluorescence studies of skin and kidney biopsies.